1. Technical Field
The present invention relates generally to the detection of intrusions into electronic assemblies, and more particularly, to the retention of a security enclosure capable of detecting such intrusions.
2. Related Art
In electronic network commerce applications, it is a requirement to protect the contents of the associated computer systems from being unlawfully read or modified. It is conventional practice to provide certain encryption schemes in which data is transmitted and received in an encrypted form and only authorized people who have the encryption key codes may read or modify the data. However, an unauthorized person with sufficient skills and knowledge may attempt to bypass software encryption controls by making a physical attack against the computer hardware to attempt a direct interrogation of the memory components and other devices. Defense from these types of attacks requires that tamper resistant physical packaging be provided for critical encryption components, in such a way that unauthorized attempts to gain entry are detected and encryption key codes are immediately erased.
One means of providing physical protection against intrusion is the use of an electrical grid surrounding the encryption module, which when broken triggers the requisite signal to disable the unit. It is known in the art to surround and protect an encryption module with a membrane consisting of one or more flexible dielectric layers having electrically conductive traces thereon. The membrane is electrically connected to the module, then wrapped, folded and bonded around the module, wherein a sticky pressure sensitive bonding adhesive adheres the membrane around the module. The traces are intentionally made fragile so that they are damaged if an attempt is made to remove the membrane. Further the membrane may be potted in a molding material, which offers further protection as its removal would also damaged the traces.
While the membrane must meet the physical security requirements, it must not be so sensitive that it falsely triggers the erasure of the key codes as a result of handling during the manufacturing assembly process, or subsequently due to environmental conditions associated with changes in temperature, humidity or atmospheric pressure. Accordingly, one of the drawbacks in the current art is that the security membranes intended for wrapping, folding, and bonding to an enclosure may be too stiff to readily fold as a result of the thickness and other properties of the various layers. As a result, during the assembly folding process, a fold may be completed but the stiffness of the membrane may result in poor retention of the fold, as the elastic strain energy associated with bending the membrane overwhelms the adhesive strength of the bonding adhesive. This can result in two conditions. First, the unfolding can damage the fragile circuit traces as the adhesive pulls against them during unfolding of the membrane. Second, unfolding can produce the formation of openings or tunnels through which the subsequently applied molding materials may leak into the interior of the enclosure, resulting in the possibility of an immediate failure or potentially a reduction in reliability of the internal components.
Thus, there is a need for better means for performing the assembly wrapping, folding, and bonding operation in such a way that the membrane is not damaged, and that molding material can not subsequently leak into the interior of the enclosure. Contrary to meeting this requirement stands the fact that the available membrane materials have certain physical properties associated with their materials selection and cross-sections that can not be readily altered, and further the fact the conductive traces are intentionally fragile so as to detect any security attack.